Alkaline battery and method for producing the same

ABSTRACT

There is provided an alkaline battery produced by sealing in an outer package body: a positive mixture containing at least one selected from manganese dioxide and a nickel oxide, a conducting agent, and an alkaline electrolytic solution (A) containing potassium hydroxide; a separator; and a negative mixture containing zinc alloy powder, a gelling agent, and an alkaline electrolytic solution (B) containing potassium hydroxide where a concentration of potassium hydroxide of the alkaline electrolytic solution (A) is 45 wt % or more, and a concentration of potassium hydroxide of the alkaline electrolytic solution (B) is 35 wt % or less. Because of this, an alkaline battery can be provided, which has desirable load characteristics, prevents the generation of gas, prevents a decrease in a storage property due to the reaction with an electrolytic solution, and has heat generation behavior suppressed at a time of occurrence of a short-circuit.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an alkaline battery having desirableload characteristics and a method for producing the same.

2. Description of the Related Art

An alkaline battery containing zinc as a negative active material isused as a power source of various kinds of electronic equipment, and isrequired to have various characteristics depending upon its use.Particularly, in a digital camera that has been widely spread in recentyears, in order to maximize the number of photographs, it is necessaryto increase the capacity of a battery and further enhance loadcharacteristics such as large current discharging characteristics.Design of a battery that can satisfy the requirements has been studied.

In order to increase the capacity of a battery, it is necessary toincrease the amount of an active material. However, if the activematerial is not used effectively for discharging, an increase in thecapacity of a battery cannot be achieved. Therefore, the above objectcannot be achieved merely by increasing the amount of the activematerial. The discharge capacity is dependent on the utilization factorof the active material, so that it is important to ensure satisfactoryconductivity of the active material and to uniformly fill the batterywith the active material. Also, it is necessary that a positiveelectrode, a negative electrode, and an electrolytic solution aredesigned so as to allow a discharging reaction to proceed smoothly.

Furthermore, in order to enhance load characteristics, it is necessaryto increase a reaction area of the active material and to enhanceconductivity. Along with an increase in the reaction area of the activematerial, gas is likely to be generated due to the reaction with anelectrolytic solution. Therefore, zinc, which is in a negative electrodeand is a negative active material, generally is formed into an alloywith an additive element capable of suppressing the generation of gas.

However, due to the increase in the battery's content of the additiveelement, conductivity is likely to be decreased. Therefore, it isdifficult to satisfy both the suppression of the generation of gas andload characteristics. Furthermore, a zinc compound (in particular, zincoxide) generally is contained in an electrolytic solution so as tosuppress self-discharging, which may decrease load characteristics.

Furthermore, even if a battery with desirable load characteristics canbe designed, another problem described below occurs, so that there stillremain problems to be solved in order to obtain a practical battery.More specifically, the storage property at high temperature may bedegraded, a battery may be short-circuited erroneously or by themalfunction of electronic equipment. Accordingly, when an excess currentflows through a battery, the temperature of the battery increases due tothe heat generated therein, which may cause leakage of an electrolyticsolution and a rupture of the battery. In particular, as a capacity of abattery is increased and a battery is designed for a higher load, thereactivity of an electrode is increased, and the amount of heatgeneration is increased.

SUMMARY OF THE INVENTION

In an embodiment of the present invention, an alkaline battery isdesigned that has desirable storage properties and is unlikely to havean abnormal behavior such as a rapid increase in temperature due to heatgeneration caused by, for example, a short-circuit, while havingdesirable load characteristics with a high capacity.

An embodiment of the present invention includes an alkaline batteryproduced by sealing in an outer package body: a positive mixturecontaining at least one selected from manganese dioxide and a nickeloxide, a conducting agent, and an alkaline electrolytic solution (A)containing potassium hydroxide; a separator; and a negative mixturecontaining zinc alloy powder, a gelling agent, and an alkalineelectrolytic solution (B) containing potassium hydroxide, wherein aconcentration of potassium hydroxide of the alkaline electrolyticsolution (A) is 45 wt % or more, and a concentration of potassiumhydroxide of the alkaline electrolytic solution (B) is 35 wt % or less.

Furthermore, an embodiment of the present invention includes a methodfor producing an alkaline battery, including: disposing a positivemixture containing at least one selected from manganese dioxide and anickel oxide, a conducting agent, and an alkaline electrolytic solution(A) containing potassium hydroxide in an outer package body;

disposing a separator inside the positive mixture;

introducing an alkaline electrolytic solution (C) containing potassiumhydroxide in a concentration of 20 to 40 wt % into the outer packagebody; and

filling a gap inside the separator with a negative mixture containingzinc alloy powder, a gelling agent, and an alkaline electrolyticsolution (B) containing potassium hydroxide,

wherein a concentration of potassium hydroxide of the alkalineelectrolytic solution (A) is 45 wt % or more, and a concentration ofpotassium hydroxide of the alkaline electrolytic solution (B) is 35 wt %or less.

Furthermore, an embodiment of the present invention includes a methodfor producing an alkaline battery, using a positive mixture obtained bymixing at least one selected from manganese dioxide and a nickel oxide,a conducting agent, and an alkaline electrolytic solution containingpotassium hydroxide in a concentration exceeding 50 wt % at atemperature in a range of 35° C. to 70° C.

Furthermore, an embodiment of the present invention includes an alkalinebattery including a positive mixture containing at least one selectedfrom manganese dioxide and a nickel oxide as a positive active materialand a negative mixture containing a negative active material, whereinthe positive mixture contains an alkaline electrolytic solutioncontaining potassium hydroxide, and an amount of water contained in thepositive mixture is 8.4 to 10 wt % with respect to a total weight of thepositive mixture including the alkaline electrolytic solution.

Furthermore, an embodiment of the present invention includes a methodfor producing an alkaline battery, using a positive mixture containingat least one selected from manganese dioxide and a nickel oxide as apositive active material and an alkaline electrolytic solutioncontaining potassium hydroxide, wherein an amount of potassium hydroxidecontained in the positive mixture used for assembly of the battery is2.4 to 4 wt % with respect to a total weight of the positive mixtureincluding the alkaline electrolytic solution, and an amount of watercontained in the positive mixture after assembly of the battery is 8.4to 10 wt % with respect to a total weight of the positive mixtureincluding the alkaline electrolytic solution.

Furthermore, an embodiment of the present invention includes a methodfor producing an alkaline battery, using a positive mixture containingat least one selected from manganese dioxide and a nickel oxide as apositive active material and an alkaline electrolytic solutioncontaining potassium hydroxide,

wherein an amount of water contained in the positive mixture used forassembly of the battery is 3.0 to 4.2 wt % with respect to a totalweight of the positive mixture including the alkaline electrolyticsolution, and an amount of water contained in the positive mixture afterassembly of the battery is 8.4 to 10 wt % with respect to a total weightof the positive mixture including the alkaline electrolytic solution.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an entire configuration of analkaline battery using a negative terminal plate as a support memberthat supports a sealing member from inside, in accordance with anembodiment of the present invention.

FIG. 2 is a cross-sectional view showing a general configuration of analkaline battery using a metal washer made of a disk-shaped metal plateas a support member that supports a sealing member from inside.

FIG. 3 is a graph showing changes in a short-circuit current and asurface temperature of an outer package can when an alkaline battery ofExample 1-3 is short-circuited.

FIG. 4 is a graph showing changes in a short-circuit current and asurface temperature of an outer package can when an alkaline battery ofComparative Examples 1-1 is short-circuited.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1

An example of an alkaline battery of the present invention has a firstfeature in that an alkaline electrolytic solution (A) containingpotassium hydroxide in a high concentration of 45 wt % or more is usedfor forming a positive mixture. The positive mixture is formed by mixingat least one of manganese dioxide and a nickel oxide, a conductingagent, and the above alkaline electrolytic solution (A). By setting theconcentration of potassium hydroxide of the alkaline electrolyticsolution (A) to be 45 wt % or more, a uniform mixed material is formedsuch that the mixture may provide a high density fill and enhance theconductivity of the entire mixture. Thus, a battery with a high capacitycan be designed, and load characteristics can be enhanced.

On the other hand, in the case where a battery is short-circuited due tothe enhanced reactivity of a positive electrode, an excess short-circuitcurrent flows immediately after the occurrence of the short-circuit.However, the rapid discharging reaction of zinc alloy powder of anegative electrode occurs, so that an oxide layer suppressing thereaction is formed on the surface of the zinc alloy powder immediately,which decreases the short-circuit within a short period of time.Therefore, the heat generated during discharging is relativelydecreased, and an increase in temperature of the battery is suppressed,which can prevent abnormal behavior such as leakage of an electrolyticsolution and a rupture of the battery. If an alkaline electrolyticsolution is used, which contains potassium hydroxide in a concentrationexceeding 50 wt % as the above-mentioned alkaline electrolytic solution(A), the above effect is likely to be obtained. In addition, anelectrolytic solution containing potassium hydroxide in a lowerconcentration can be used as an alkaline electrolytic solution (B) of anegative mixture (described later), so that particularly desirableeffects can be obtained.

The saturation concentration of potassium hydroxide at room temperatureis about 50 wt %. Therefore, in the case of using an alkalineelectrolytic solution in a concentration higher than 50 wt %, it isdesirable to manage the temperature of the mixture. More specifically,the alkaline electrolytic solution generally is prepared under warmconditions so that potassium hydroxide is likely to be dissolved.Therefore, it is easy to prepare a potassium hydroxide aqueous solutionin a concentration exceeding 50 wt %. However, in the case where themixture is prepared at about room temperature or lower, potassiumhydroxide is deposited exceeding the saturation amount at thattemperature, which may impair the formation of a uniform mixture.Therefore, it is desirable to prepare a mixture constituent in a warmenvironment so that the electrolytic solution does not reach thesaturation concentration, thereby producing a positive mixture. Thetemperature condition desirably is 35° C. or higher so as to enhance thesaturation solution amount of potassium hydroxide, and desirably is 70°C. or lower so as to prevent the composition of the electrolyticsolution from changing due to the evaporation of water. Furthermore,even in the case where the concentration of potassium hydroxide is 45 to50 wt %, by preparing a mixture constituent in a warm environment, thedispersibility of the constituent is enhanced and a uniform mixture islikely to be formed.

As the above-mentioned conducting agent, a carbon material such asgraphite, acetylene black, carbon black, and fibrous carbon mainly canbe used. Among them, graphite is preferably used. As the positive activematerial, either one of manganese dioxide, nickel oxyhydroxide, and anickel oxide such as a compound in which another element is substitutedfor a part of nickel, or a combination thereof is used. It is desirablethat graphite is mixed in a ratio of 6 wt % or more with respect to thetotal weight of manganese dioxide and a nickel oxide that are positiveactive materials. The reason for this is that the above-mentioned effectof suppressing abnormal generation of heat at a time of occurrence of ashort-circuit can be achieved. On the other hand, a decrease in anamount of the active material is not preferable, so that the ratio ofgraphite desirably is set to be 8.5 wt % or less.

A small amount of a binder such as carboxymethyl cellulose, methylcellulose, polyacrylate, polytetrafluoroethylene, and polyethylene alsocan be contained in the positive mixture. When the additional amount ofthe binder is large, conductivity is decreased, and the like; however,when the additional amount thereof is small, the contact between theconducting agent and the active material is satisfactory.

Furthermore, an embodiment of the present invention of the alkalinebattery has a second feature in that an alkaline electrolytic solution(B) containing potassium hydroxide in a concentration of 35 wt % or lessis used for forming a negative mixture. The negative mixture is formedby mixing zinc alloy powder, a gelling agent, and an alkalineelectrolytic solution (B) in which potassium hydroxide is dissolved toform a gel mixed material. By setting the concentration of potassiumhydroxide of the alkaline electrolytic solution (B) to be 35 wt % orless, the state of an oxide coating on the surface of zinc alloy powdercan be appropriately made, the conductivity of the alkaline electrolyticsolution is increased to enhance load characteristics, and a dischargingreaction proceeds as desired in an initial stage of a short-circuit.Therefore, the above-mentioned effect of suppressing abnormal generationof heat can be obtained.

In particular, it is desirable that indium, bismuth, and aluminum areincluded as alloy elements of zinc alloy powder. This is because theseelements make a preferable surface state of the zinc alloy powder, andhave an effect of enhancing load characteristics and suppressingabnormal generation of heat. Furthermore, the addition of these elementsincreases a reaction area of the zinc alloy powder, so that even whenthe ratio of minute particles is increased, the reaction with anelectrolytic solution is suppressed to prevent the generation of gas. Itis desirable that the contents of indium, bismuth, and aluminumrespectively are 0.03 to 0.07 wt %, 0.007 to 0.025 wt %, and 0.001 to0.004 wt %. If the ratio of the minute particles that pass through a200-mesh sieve is 4 wt % or more with respect to the total weight of thezinc alloy powder, the characteristics during pulse discharging at alarge current are further enhanced, which is preferable. The ratio ofthe minute particles more desirably is 15 wt % or more. On the otherhand, in order to form a uniform negative mixture having satisfactoryflowability, the ratio of the minute particles desirably is 40 wt % orless.

Furthermore, by allowing the alkaline electrolytic solution (B) tocontain a zinc compound, a preferable surface state of the zinc alloypowder also can be made. As the zinc compound, zinc oxide, zincsilicate, zinc titanate, zinc molybdate, and the like can be used. Zincoxide preferably is used. In order to increase the solubility of thezinc compound, it is desirable that the concentration of potassiumhydroxide of the alkaline electrolytic solution (B) is set to be 20 wt %or more. A zinc compound may be contained in the alkaline electrolyticsolution (A) in a positive mixture or an alkaline electrolytic solution(C) descried later.

An indium compound such as indium oxide and a bismuth compound such asbismuth oxide can be contained in a small amount in a negative mixture.In the case where these compounds are contained in the negative mixture,the generation of gas due to the reaction between the zinc alloy powderand the electrolytic solution can be effectively further prevented.However, these compounds may decrease load characteristics, so that thecontents thereof are determined as required.

An example of the alkaline battery of the present invention is producedby sealing the above-mentioned positive mixture and the above-mentionednegative mixture in an outer package body together with a separator. Aninsufficient amount of liquid may occur with the alkaline electrolyticsolution contained in the positive mixture and the negative mixture. Inthis case, the process of further injecting an electrolytic solution soas to be absorbed by the separator is required. As an alkalineelectrolytic solution (C) to be injected at this time, a solution inwhich potassium hydroxide is dissolved in a concentration of 20 to 40 wt% is preferably used. More specifically, the above-mentioned effect ofsuppressing abnormal generation of heat at a time of occurrence of ashort-circuit also depends upon the concentration of potassium hydroxideof the alkaline electrolytic solution (C). It is desirable that anelectrolytic solution in a lowest possible concentration is used. If theconcentration is less than 35 wt %, better results are obtained. On theother hand, after the assembly of a battery, the alkaline electrolyticsolutions (A), (B), and (C) in the battery diffuse to be mixed with eachother to become a uniform electrolytic solution gradually. In this case,it is desirable that the concentration of each potassium hydroxide ofthe alkaline electrolytic solutions (A), (B), and (C) is adjusted sothat the average concentration of potassium hydroxide of the entirealkaline electrolytic solution is in a preferable range. It also isdesirable that potassium hydroxide is contained in a concentration of 20wt % or more in the alkaline electrolytic solution (C).

Furthermore, if a zinc compound is contained in the alkalineelectrolytic solutions (A) and (C), as well as in the alkalineelectrolytic solution (B), the effect of reducing the degradation ofbattery's characteristics are enhanced when the battery is stored athigh temperature. If the concentration of potassium hydroxide of thealkaline electrolytic solution (C) is set to be 20 wt % or more, thesolubility of the zinc compound is increased, which also is convenientin terms of the addition of the zinc compound.

It is desirable to design a battery so that the average concentration ofpotassium hydroxide in the entire alkaline electrolytic solution becomes30 to 37 wt %. The reason for this is as follows. The storage propertyis enhanced during storage at high temperature by setting theconcentration of potassium hydroxide to be 30 wt % or more, andpreferable characteristics are obtained at a concentration of 33.5 wt %or more. On the other hand, when the average concentration is set to be37 wt % or less, load characteristics are enhanced, and the effect ofsuppressing abnormal generation of heat at a time of occurrence of ashort-circuit is likely to be obtained.

In the present embodiment, the shape of a battery is not particularlylimited. In the case of using a cylindrical metal outer package can asan outer package body, the above-mentioned positive mixture molded in aring shape is placed in the outer package can, a cup-shaped separator isplaced in the positive mixture, then, the alkaline electrolytic solution(C) is injected so as to be absorbed by the separator, a gap inside theseparator is filled with the above-mentioned negative mixture, and thesecomponents are sealed in the outer package can, whereby a battery isassembled. As shown in FIG. 2, in a cylindrical alkaline battery, anopen end (1 a) of an outer package can (1) is bent inward to performsealing, a metal washer (9) made of a disk-shaped metal plate generallyis used as a support member for preventing the deformation of a negativeterminal plate (207) and supporting a sealing member (6) from inside.However, there is a problem that the volume occupied by a sealingportion (10) is increased.

On the other hand, in a battery shown in FIG. 1 using a negativeterminal plate (7) as the support member for supporting the sealingmember (6) from inside without using a metal washer, the volume occupiedby the sealing portion (10) can be decreased. Accordingly, heatgeneration at a time of occurrence of a short-circuit is increased alongwith an increase in capacity of a battery while the amount of themixtures of a positive electrode (2) and a negative electrode (4) can beincreased. However, even in such a battery designed so as to have a highcapacity, according to the present invention, abnormal generation ofheat in the battery can be prevented, so that the practicability of thebattery can be enhanced.

Next, examples of the present embodiment will be described. The presentinvention is not limited to these examples.

EXAMPLE 1-1

Electrolytic manganese dioxide, graphite, polytetrafluoroethylenepowder, and an alkaline electrolytic solution (A) (56 wt % of apotassium hydroxide aqueous solution containing 2.9 wt % of zinc oxide)were mixed in a weight ratio of 87.6:6.7:0.2:5.5, whereby a positivemixture was prepared. The positive mixture was prepared at 50° C.Furthermore, the ratio of graphite with respect to manganese dioxide inthe positive mixture was 7.6 wt %.

Furthermore, zinc alloy powder containing indium, bismuth, and aluminumin a ratio of 0.05 wt %, 0.05 wt %, and 0.005 wt %, polyacrylic soda,polyacrylic acid, and an alkaline electrolytic solution (B) (32 wt % ofa potassium hydroxide aqueous solution containing 2.2 wt % of zincoxide) that were binders were mixed in a weight ratio of 39:0.2:0.2:18to prepare a gel negative mixture. The zinc alloy powder had an averageparticle size of 122 μm, was passed through a 80-mesh sieve and was notpassed through a 200-mesh sieve, and had an apparent density of 2.65g/cm³.

Next, an alkaline battery having a configuration similar to that shownin FIG. 1 was produced as follows. An outer package can (1) made of akilled steel plate for an AA alkaline battery was used, in which asealing portion (10) had a thickness of 0.25 mm, a body (20) had athickness of 0.16 mm, and in order to prevent a positive terminal (1 b)from being dented when a battery was dropped, the thickness of the outerpackage can (1) in the positive terminal (1 b) portion was made slightlythicker than that of the body (20).

Then, 11 g of the above positive mixture was molded under pressure to acylindrical shape with an inner diameter of 9.1 mm, an outer diameter of13.7 mm, and a height of 41.7 mm to obtain a positive electrode (2), andthe positive electrode (2) was inserted in the outer package can (1).Thereafter, a groove was formed at a position of 3.5 mm in the heightdirection from an open end of the outer package can (1), and in order toenhance the contact between the outer package can (1) and a sealingmember (6), the inside of the outer package can (1) was coated with apitch up to the groove position.

Next, non-woven fabric having a thickness of 100 μm, made of acetalizedvinylon fibers with a unit weight of 30 g/m² and refined cellulosefibers (Registered Trade Mark: TENCEL, produced by Tencel Inc.), waswound to a cylindrical shape. A portion to be a bottom was bent andthermally fused to obtain a cup-shaped separator (3) with one endclosed. The separator (3) was placed inside the positive electrode (2)inserted in the outer package can (1), and 1.35 g of an alkalineelectrolytic solution (C) (32 wt % of a potassium hydroxide aqueoussolution containing 2.2 wt % of zinc oxide) was injected into the outerpackage can (1) so as to penetrate the separator (3). Then, the insideof the separator (3) was filled with 5.74 g of the above negativemixture to obtain a negative electrode (4).

After filling of the above-mentioned electric generating elements, anegative current collector (5) (made of brass with a tinned surface)combined with the sealing member (6) made of Nylon 6-6 was inserted tothe central portion of the negative electrode (4). The negative currentcollector (5) was crimped by spinning from outside of the open end (1 a)of the outer package can (1) to produce an AA alkaline battery as shownin FIG. 1. Herein, the negative current collector (5) was previouslyattached to a negative terminal plate (7) made of a nickel-plated steelplate with a thickness of 0.4 mm formed by stamping. Furthermore, aninsulating plate (8) was placed between the open end (1 a) of the outerpackage can (1) and the negative terminal plate (7) so as to prevent ashort-circuit.

The alkaline electrolytic solution in the assembled battery containedpotassium hydroxide having an average concentration of 35 wt %.

EXAMPLE 1-2

An AA alkaline battery was produced in the same way as in Example 1-1,except that electrolytic manganese dioxide, graphite,polytetrafluoroethylene powder, and an alkaline electrolytic solution(A) were mixed in a weight ratio of 89.3:5.1:0.2:5.6 to prepare apositive mixture. In the positive mixture, the ratio of graphite withrespect to manganese dioxide was 5.7 wt %.

EXAMPLE 1-3

An AA alkaline battery was produced in the same way as in Example 1-1,except that 30 wt % of a potassium hydroxide aqueous solution containing2.0 wt % of zinc oxide was used as the alkaline electrolytic solutions(B) and (C). The alkaline electrolytic solution in the assembled batterycontained potassium hydroxide having an average concentration of 33 wt%.

EXAMPLE 1-4

An AA alkaline battery was produced in the same way as in Example 1-1,except that, in the zinc alloy powder of the negative electrode, zincalloy powder was used, which contained indium, bismuth, and aluminum ina ratio of 0.05 wt %, 0.015 wt %, and 0.003 wt %, had an averageparticle size of 200 μm, was passed through a 35-mesh sieve, was passedthrough a 200-mesh sieve in a ratio of 6 wt %, and had an apparentdensity of 2.9 g/cm³.

EXAMPLE 1-5

An AA alkaline battery was produced in the same way as in Example 1-1,except that, in the zinc alloy powder of the negative electrode, zincalloy powder was used, which had an average particle size of 135 μm, waspassed through a 35-mesh sieve, was passed through a 200-mesh sieve in aratio of 20 wt %, and had an apparent density of 2.9 g/cm³.

COMPARATIVE EXAMPLE 1-1

An AA alkaline battery was produced in the same way as in Example 1-1,except that 36 wt % of a potassium hydroxide aqueous solution containing2.4 wt % of zinc oxide was used as the alkaline electrolytic solutions(B) and (C). The alkaline electrolytic solution in the assembled batterycontained potassium hydroxide having an average concentration of 39 wt%.

COMPARATIVE EXAMPLE 1-2

An AA alkaline battery was produced in the same way as in Example 1-1,except that 42 wt % of a potassium hydroxide aqueous solution containing2.9 wt % of zinc oxide was used as the alkaline electrolytic solution(A). The alkaline electrolytic solution in the assembled batterycontained potassium hydroxide having an average concentration of 32 wt%.

COMPARATIVE EXAMPLE 1-3

An AA alkaline battery was produced in the same way as in ComparativeExample 1-1, except that, in the zinc alloy powder of the negativeelectrode, zinc alloy powder was used, which had an average particlesize of 195 μm, was passed through a 35-mesh sieve, did not pass througha 200-mesh sieve, and had an apparent density of 2.65 g/cm³.

A pulse discharging test was performed with respect to 12 batteries thusproduced in each of the above Examples and Comparative Examples. In thistest, a pulse current of 2A was allowed to flow for 2 seconds at aninterval of 30 seconds with a base discharging current set at 0.5 A. Thenumber of pulse discharging cycles required for a voltage, at a timewhen the pulse current of 2A flowed, to decrease to 1.0 V or less wasmeasured and averaged, whereby load characteristics were evaluated.

Furthermore, in another 12 batteries, a thermocouple was fixed to acentral portion of a side surface of the outer package can (1) of eachbattery with an aluminum tape. The surface temperature of the outerpackage can (1) when each battery was short-circuited was measured andaveraged, whereby heat generation behavior at a time of occurrence ofthe short-circuit was evaluated. At this time, in the batteries ofExample 1-3 and Comparative Example 1-1, a change in a current valuewith the passage of time also was measured. Changes in a short-circuitcurrent and in a surface temperature of the outer package can (1) fromthe commencement of a short-circuit are shown in FIG. 3 (Example 1-3)and in FIG. 4 (Comparative Example 1-1).

Furthermore, another 24 batteries were evaluated. First, 12 batteriesamong the 24 batteries were discharged at a discharging current of 1A,and a discharging time required for a voltage to decrease to 0.9 V orless was measured and averaged. The average time was determined as adischarging time before storage. Then, the remaining 12 batteries werestored in a thermostatically controlled environment at 60° C. for 20days. Thereafter, they were taken out of the thermostatically controlledenvironment and cooled at room temperature for 1 day. Then, thebatteries were discharged at a discharging current of 1A, and adischarging time required for a voltage to decrease to 0.9 V or less wasmeasured and averaged. The average time was determined as a dischargingtime after storage. The ratio of the discharging time after storage withrespect to the discharging time before storage was obtained as acapacity retention ratio, and the storage property of the batteries athigh temperature was evaluated.

Table 1 shows measurement results for the number of pulse dischargingcycles, the surface temperature of the outer package can (1), and thecapacity retention ratio. There was no particular problem involved ingeneration of gas.

TABLE 1 Number of pulse Surface temperature Capacity discharging cyclesof outer package can retention ratio (No.) (° C.) (%) Example 1-1 62 12388 Example 1-2 60 146 84 Example 1-3 68 113 81 Example 1-4 68 112 89Example 1-5 73 138 91 Comparative 60 162 90 Example 1-1 Comparative 67109 73 Example 1-2 Comparative 52 112 90 Example 1-3

As is apparent from the results in Table 1, the batteries of theExamples according to the present invention had desirable loadcharacteristics, had generation of heat suppressed at a time ofoccurrence of a short-circuit, and had desirable storage properties athigh temperature. Particularly, in the battery of Example 1-1 in whichthe ratio of graphite with respect to manganese dioxide in the positivemixture was set in a range of 6 to 8.5 wt %, and the averageconcentration of potassium hydroxide in the alkaline electrolyticsolution in the battery was set to be 33.5 wt % or more, the surfacetemperature of the outer package can was decreased more than that of thebattery of Example 1-2 in which the ratio of graphite was smaller, andthe capacity retention ratio was enhanced more than that of the batteryof Example 1-3 in which the concentration of potassium hydroxide wassmaller.

Furthermore, in the battery of Example 1-4 containing 6 wt % of powderof 200 mesh or less in the zinc alloy powder, in which the ratio of theminute particles was larger than that of Example 1-1, the content ratiosof indium, bismuth, and aluminum were optimized, whereby the number ofpulse discharging was increased without increasing the surfacetemperature of the outer package can (1) and decreasing the capacityretention ratio. Furthermore, in the battery of Example 1-5 in which theratio of the minute particles was increased, although the surfacetemperature of the outer package can was increased, the number of pulsedischarging was increased further.

On the other hand, in the battery of Comparative Example 1-1 in whichthe concentration of potassium hydroxide of the alkaline electrolyticsolution (B) of the negative mixture was set to be higher than 35 wt %,the powder of 35 to 80 mesh was removed, whereby the ratio of the minuteparticles in the zinc alloy powder was increased more than that of thebattery of Comparative Example 1-3. Therefore, the number of pulsedischarging was increased more than that of Comparative Example 1-3 inthe same way as in Example 1-1; however, the surface temperature of theouter package can (1) was increased substantially compared with that ofthe battery of Example 1-1. Furthermore, in the battery of ComparativeExample 1-2 in which the concentration of potassium hydroxide of thealkaline electrolytic solution (A) of the positive mixture was set to beless than 45 wt %, the capacity retention ratio was decreasedsubstantially. Thus, in either case, practical characteristics were notobtained.

As described above, the present embodiment can provide an alkalinebattery that has desirable load characteristics, prevents the generationof gas and a decrease in a storage property due to the reaction with anelectrolytic solution, and has heat generation behavior suppressed at atime of occurrence of abnormality and, a method for producing the same.

Embodiment 2

A discharging reaction of a positive electrode of an alkaline batteryusing manganese dioxide as a positive active material proceeds inaccordance with the following Formula (1):Positive electrode: MnO₂+H₂O+e ⁻→MnOOH+OH⁻  (1)

As is apparent from the above Formula (1), water is consumed duringdischarging at the positive electrode. Therefore, it is desirable thatwater is present as much as possible on the positive electrode side inthe battery in terms of a discharging reaction. This also applies to thecase where a nickel oxide such as nickel oxyhydroxide is used as apositive active material.

Regarding the water amount in the positive mixture, it has beenconventionally proposed that the ratio of water contained in thepositive mixture is set to be 3.5 to 5.0%, and the weight of a potassiumhydroxide electrolytic solution contained in the positive mixture afterforming a battery is set to be 10.6 to 15.9 wt % with respect to thetotal solid weight in the positive mixture. Furthermore, it also hasbeen proposed that the additional amount of water in the entire batteryis set to be 0.947 to 1.146 g based on 1 AH of theoretical dischargecapacity of manganese dioxide in terms of safety and dischargingcharacteristics. This corresponds to the addition of 0.292 to 0.353 g ofwater based on 1 g of active material, which is very high compared withthe water amount (0.207 g) required for a discharging reaction of 1 g ofmanganese dioxide.

However, in the range of the amount of the electrolytic solution in thepositive mixture, the above water amount is not sufficient, so thatsatisfactory characteristics cannot be obtained at heavy load. On theother hand, when the required water is contained previously in apositive mixture during assembly of a battery, the filling density of anactive material is decreased, which makes it impossible to avoid adecrease in capacity. Furthermore, water comes out of the mixture duringmolding, and the molding strength is lowered to make it difficult tomold the mixture. This causes problems in terms of production.Therefore, it is desirable that the water amount contained in themixture is minimized during forming of the positive mixture.

More specifically, it is required that the water amount in the positivemixture to be used for assembling a battery is minimized, while thewater amount in the positive mixture is maximized after assembling abattery.

The inventors of the present invention did not satisfy the aboverequirement merely by adjusting the ratio of water contained in thepositive mixture and the additional amount of water in the entirebattery. The inventors found it desirable to require that an amount ofwater be moved from the separator or the negative electrode side to thepositive mixture after assembling a battery. Furthermore, they foundthat by appropriately distributing water in a battery, the additionalamount of water in the entire battery can be decreased, and a storageproperty is not degraded at high temperature because of the absence ofexcess water.

The present embodiment provides an alkaline battery having desirableload characteristics, safety at a time of occurrence of a short-circuit,and a storage property at high temperature by allowing a positivemixture after assembly of a battery to contain a sufficient amount ofwater required for a reaction, and a method for producing such analkaline battery.

By assembling an alkaline battery using the above production method, asufficient amount of water required for a discharging reaction can becontained in a positive mixture after assembly of a battery, and wateris appropriately distributed in the battery. Therefore, an alkalinebattery can be obtained, which has desirable load characteristics andsafety at a time of occurrence of a short-circuit and in which a storageproperty is less degraded at high temperature, even when the watercontent in the entire battery is small.

An example of the alkaline battery of the present invention ischaracterized in that the amount of water contained in a positivemixture is 8.4 to 10 wt % with respect to the total weight of thepositive mixture including an alkaline electrolytic solution afterassembly of a battery. Therefore, it is required that a relatively largeamount of water moves from a separator or a negative electrode side to apositive electrode. In order to allow water to move in this manner, adriving force is required. As a method for generating a driving force,for example, a large difference was previously provided in an alkalineconcentration between the electrolytic solution contained in a positivemixture and the electrolytic solution injected during assembly or theelectrolytic solution contained in the negative mixture, and afterassembly, water in the separator or on the negative electrode side ismoved to the positive mixture due to the difference in concentration.

The positive electrode of the present embodiment is obtained by mixingone selected from manganese dioxide and a nickel oxide, a conductingagent, and an alkaline electrolytic solution containing potassiumhydroxide, and molding the mixture thus obtained, in the same way as inEmbodiment 1. By setting the concentration of potassium hydroxide of analkaline electrolytic solution to be added for forming a mixture to behigher than 50 wt %, the driving force becomes large, and a large amountof water can be taken in the positive mixture. Furthermore, thisenhances the binding force of the mixture to form a uniform mixedmaterial, so that it also is possible to fill an active material at highdensity. At this time, the density of the positive mixture may be set tobe 3.2 to 3.35 g/cm³. Because of this, while a required amount of anactive material is kept, a large amount of water can be contained.

Manganese dioxide and a nickel oxide that are positive active materialsgenerally contain a certain amount of water due to adsorption.Therefore, the concentration of potassium hydroxide of the alkalineelectrolytic solution contained in the mixture is lower than that of thealkaline electrolytic solution to be added first. Therefore, regardingthe water amount, water derived from the positive active material shouldbe considered, and it is desirable that the concentration of an alkalineelectrolytic solution to be added to a mixture is set so that theconcentration of potassium hydroxide of the alkaline electrolyticsolution contained in the final mixture is 40 wt % or more.

Furthermore, regarding the additional amount of the alkalineelectrolytic solution, the weight of potassium hydroxide is desirably ina range of 2.4 to 4 wt % with respect to the weight of the entiremixture including the alkaline electrolytic solution contained in themixture, and the water amount is desirably in a range of 3.0 to 4.2 wt%. Because of this, an appropriate driving force is obtained, and thewater amount after assembly of a battery can be easily adjusted to anappropriate range.

In the case of setting the concentration of potassium hydroxide of thealkaline electrolytic solution higher than 50 wt % in the production ofthe above-mentioned positive mixture, it is desirable that a positivemixture is produced in a warm environment of 35° C. to 70° C. in thesame way as in Embodiment 1.

Alternatively, depending upon the purpose, a conducting agent, a binder,and the like can be contained in the positive mixture. As the conductingagent, a carbon material such as graphite, acetylene black, carbonblack, and fibrous carbon mainly can be used. Among them, graphite isused preferably in the same way as in Embodiment 1. The additionalamount of the conducting agent is desirably 3 wt % or more with respectto the total weight of the positive active material. Because of this,sufficient water is contained in the positive mixture, and theconductivity of a positive electrode is enhanced, whereby the reactivityof the active material is enhanced, and further enhancement of loadcharacteristics can be expected. On the other hand, a decrease in anamount of an active material is not preferable. Therefore, the ratio ofthe conducting agent is desirably set to be 8.5 wt % or less.

Furthermore, as the binder, carboxymethyl cellulose, methyl cellulose,polyacrylate, polytetrafluoroethylene, polyethylene, and the like can beused in the same way as in Embodiment 1.

In the present embodiment, the reactivity of the positive electrode isenhanced, whereby another effect described below can be expected to beobtained in the same way as in Embodiment 1. More specifically, in thecase where abnormality occurs (e.g., a battery is short-circuited bymistake), a large short-circuit current continues to flow. Therefore,the temperature of a battery is rapidly increased due to the generationof heat caused by the flow of a large short-circuit current, wherebyleakage and rupture of a battery are likely to be caused. On the otherhand, in the battery of the present embodiment, a discharging reactionproceeds more rapidly at a positive electrode than a conventionalbattery, so that a discharging reaction at a negative electrode alsoproceeds rapidly. After occurrence of a short-circuit, a large amount ofa discharging product is deposited on the surface of a negativeelectrode to suppress a discharging reaction. As a result, ashort-circuit current is decreased within a short period of time, and anincrease in temperature of the battery is suppressed, which can preventthe above-mentioned problems.

The driving force for moving water to the positive electrode is notdetermined solely by the configuration of the positive electrode, and isclosely related to other components such as a negative electrode, inparticular, to the concentration of potassium hydroxide of anelectrolytic solution separately injected into an outer package body andan electrolytic solution contained in a negative mixture. Therefore, itis desirable that the configurations thereof are also optimized. Morespecifically, if either one of the electrolytic solution to be injectedand the electrolytic solution contained in the negative mixture, ordesirably both of them have a low alkaline concentration, the abovedriving force becomes large, and more desirable results are obtained.

Hereinafter, the configuration of a negative electrode will bedescribed. The negative electrode generally is formed as a gel mixtureobtained by mixing zinc or zinc alloy powder that is an active material,a gelling agent, and an alkaline electrolytic solution in whichpotassium hydroxide is dissolved. At this time, it is desirable that theconcentration of potassium hydroxide of the electrolytic solution of thenegative electrode is 38 wt % or less. As the alkaline concentration ofthe electrolytic solution is lower, the water content becomes high,whereby the water amount required in the entire battery can be adjustedeasily. Furthermore, in order to increase the ion conductivity of theelectrolytic solution to enhance the reactivity of the negativeelectrode, so as to enhance load characteristics and make it easy toobtain a heat generation suppressing effect at a time of occurrence of ashort-circuit, the concentration of potassium hydroxide is set to bedesirably 35 wt % or less, and more desirably 33.5 wt % or less. On theother hand, as the concentration of potassium hydroxide is increased,characteristics are less degraded when a battery is stored at hightemperature. Therefore, the concentration of potassium hydroxide is setto be desirably 28 wt % or more, and more desirably 30 wt % or more.

Furthermore, in order to handle heavy loads such as pulse discharging ata large current, it is desirable that the particle diameter of an activematerial is decreased to increase a reaction area. For example, theratio of active material powder passing through a 200-mesh sieve shouldbe set to be 4 wt % or more, and when the ratio is set to be 15 wt % ormore, load characteristics are remarkably enhanced. On the other hand,in order to form a uniform negative mixture with satisfactoryflowability, the ratio of the minute particles desirably is set to be 40wt % or less. Thus, in the case where minute particles are contained ina predetermined ratio, problems such as the generation of gas due to thereaction between the active material and the electrolytic solution, adecrease in a discharge capacity, and the like are likely to occurduring storage at high temperature. In order to prevent this, elementssuch as indium, bismuth, and aluminum may be added to zinc. The contentsof indium, bismuth, and aluminum are desirably 0.03 to 0.07 wt %, 0.007to 0.025 wt %, and 0.001 to 0.004 wt %, respectively. Furthermore, asthe particle diameter is smaller, the generation of heat at a time ofoccurrence of a short-circuit becomes a serious problem. In the presentembodiment, even in the case where the described minute particles areused, the effect of suppressing the generation of heat can be exhibitedsufficiently.

An indium compound such as indium oxide and a bismuth compound such asbismuth oxide can be contained in the negative mixture in a small amountin the same way as in Embodiment 1.

An alkaline battery of the present embodiment is produced by sealing theabove-mentioned positive mixture and negative mixture in an outerpackage body together with a separator. The liquid amount isinsufficient only with the alkaline electrolytic solution contained inthe positive mixture and the negative mixture. Therefore, the process offurther injecting an electrolytic solution so as to be absorbed by theseparator and the positive electrode is required in the same way as inEmbodiment 1. In the alkaline electrolytic solution to be injected atthis time, a solution in which potassium hydroxide is dissolved in aconcentration of 35 wt % or less is desirably used so as to increase thecontent of water to increase the supply of water to the positiveelectrode. Furthermore, it is desirable that the concentration ofpotassium hydroxide is 33.5 wt % or less in terms of enhancement of loadcharacteristics and suppression of heat generation at a time ofoccurrence of a short-circuit. On the other hand, as the concentrationof potassium hydroxide is increased, characteristics degrade less when abattery is stored at high temperatures. Therefore, the concentration ofpotassium hydroxide is desirably 28 wt % or more, and more desirably 30wt % or more.

Furthermore, in order to enhance the effect of preventing degradation ofcharacteristics during storage at high temperatures, it is desirablethat a zinc compound is contained in at least one of the electrolyticsolution used for forming a positive mixture, the electrolytic solutionused for forming a negative mixture, and the electrolytic solution to beinjected separately in the same way as in Embodiment 1. As the zinccompound, a soluble compound such as zinc oxide, zinc silicate, zinctitanate, and zinc molybdate can be used. In particular, zinc oxide ispreferably used.

After assembly of a battery, water moves from the injected electrolyticsolution or the electrolytic solution in the negative mixture to thepositive electrode side. Then, the water is absorbed by the positivemixture, and the water amount in the mixture is increased. The change inthe water amount depends upon the conditions such as a storagetemperature of a battery. Therefore, the change in the water amount maybe completed about 1 to 3 months after assembly of a battery.Thereafter, the water amount in the mixture is assumed to be maintainedat a constant value. In this state, the composition and additionalamount of each electrolytic solution used for the above-mentionedpositive electrode, negative electrode and injection should be adjustedso that the water amount contained in the positive mixture is 8.4 to 10wt % with respect to the weight of the entire positive mixture includingthe electrolytic solution. In the case where the water amount is lessthan 8.4 wt %, problems occur in any of the load characteristics, heatgeneration at a time of occurrence of a short-circuit, and storagecharacteristics at high temperature. Furthermore, in the case where thewater amount is larger than 10 wt %, the amount of the electrolyticsolution contained in the positive mixture is in excess. Consequently,the conductivity is decreased due to the swelling of the mixture, andshortage of the amount of the electrolytic solution on the separatorside is caused. Thus, there are problems in the battery'scharacteristics.

Furthermore, the water amount of the electrolytic solution contained inthe positive mixture after assembly of a battery and the concentrationof potassium hydroxide are obtained by disassembling the battery toanalyze the positive mixture. For example, the water amount can beobtained from the weight change when the positive mixture is dried in anatmosphere excluding the influence of carbonic acid gas, such as invacuum or an atmosphere of inactive gas. Furthermore, the concentrationof potassium hydroxide can be obtained as (amount of potassiumhydroxide)/(amount of potassium hydroxide+water amount) by obtaining theamount of potassium hydroxide from a measurement value of the amount ofpotassium in the mixture, assuming that the measurement value is allderived from potassium hydroxide. The concentration of potassiumhydroxide desirably is 35 to 39.5 wt %. The composition of theelectrolytic solution in the positive mixture is not necessarily matchedwith the composition of the electrolytic solution in the negativemixture. Even in a state where the alkaline concentration in thepositive mixture is higher, water movement to the positive electrode iscompleted, and this state may be maintained.

In the present embodiment, as described above, a sufficient amount ofwater is contained in the positive mixture, whereby water is distributedappropriately in the battery. Therefore, the total water amount in thebattery can be made smaller (0.23 to 0.275 g based on 1 g of positiveactive material) than that of the conventional example. Therefore,excess water is not present in the battery, and characteristics are lessdegraded when a battery is stored at high temperature. On the otherhand, water required for a reaction is ensured, so that a batteryexhibiting excellent operation characteristics can be obtained.

Furthermore, in the present embodiment, there is no particular limit tothe shape of a battery in the same way as in Embodiment 1.

Hereinafter, examples of the present embodiment will be described. Thepresent invention is not limited to these examples.

EXAMPLE 2-1

An alkaline battery was produced in the same way as in Example 1-1,except that electrolytic manganese dioxide containing 1.6 wt % of water,graphite, polytetrafluoroethylene powder, and an alkaline electrolyticsolution (56 wt % of potassium hydroxide aqueous solution containing 2.9wt % of zinc oxide) for forming a positive mixture were mixed in aweight ratio of 87.6:6.7:0.2:5.5 at 50° C., and a positive mixture witha density of 3.21 g/cm³ was used. In this mixture, the weight ratio ofgraphite with respect to the total weight of manganese dioxide was 7.6wt %.

The concentration of potassium hydroxide contained in the positivemixture was 44.6 wt % considering the water contained in manganesedioxide, and the amount of potassium hydroxide and the water amount were3.1 wt % and 3.7 wt %, respectively, with respect to the total weight ofthe positive mixture containing an electrolytic solution. Furthermore,the total water amount in the battery at this time was 0.261 g based on1 g of a positive active material.

Regarding the batteries of Example 2-1 produced as described above, 5batteries were disassembled, respectively, 1 month, 3 months, and 6months after assembly of the batteries, and the amounts of potassium andwater contained in the positive mixtures were obtained by the followingmethod.

More specifically, each disassembled battery was separated into apositive electrode and an outer package can, and a negative electrodeand a separator, and the weight of the positive electrode and the outerpackage can was measured. The positive electrode and the outer packagecan were dried at 110° C. for 12 hours in vacuum, and the water amountcontained in the positive mixture was obtained from the differencebetween the weight before drying and the weight after drying. Then, thedried positive mixture was taken out, manganese dioxide was dissolved inan acid, and the weight of potassium was obtained by atomic absorptionspectrometry with respect to a solution with a residue removedtherefrom. Assuming that the atomic weight of potassium is 39.1, and theformula weight of potassium hydroxide (KOH) is 56.1, the amount ofpotassium hydroxide was obtained from the amount of potassium byconversion of potassium hydroxide amount=potassium amount×(56.1/39.1).Furthermore, the concentration of potassium hydroxide was obtained withrespect to the alkaline electrolytic solution contained in the positivemixture after assembly of a battery, from the formula of concentrationof potassium hydroxide=amount of potassium hydroxide/(potassiumhydroxide amount+water amount).

Table 2-1 shows an average value of each battery with respect to thewater amount and the concentration of potassium hydroxide. The followingis understood from Table 2-1: one month after assembly of a battery,required water was taken in a positive mixture; and three months afterassembly, the water amount was not changed and this state wasmaintained.

TABLE 2-1 Concentration of Period from potassium hydroxide assembly ofbattery Water amount (wt %) (wt %) 1 month 8.6 37.8 3 months 8.9 38.0 6months 8.9 38.0

EXAMPLE 2-2

An AA alkaline battery was produced in the same way as in Example 2-1,except that 30 wt % of potassium hydroxide aqueous solution containing2.0 wt % of zinc oxide was used as an alkaline electrolytic solution forforming a negative mixture and an alkaline electrolytic solution forinjection. At this time, the total amount water in the battery was 0.268g based on 1 g of positive active material.

EXAMPLE 2-3

An AA alkaline battery was produced in the same way as in Example 2-1,except that, as the zinc alloy powder of the negative electrode, zincalloy powder was used, which contained indium, bismuth, and aluminum ina ratio of 0.05 wt %, 0.015 wt %, and 0.003 wt %, had an averageparticle size of 200 μm, was passed through a 35-mesh sieve, was passedthrough a 200-mesh sieve in a ratio of 6 wt %, and had an apparentdensity of 2.9 g/cm³.

EXAMPLE 2-4

An AA alkaline battery was produced in the same way as in Example 2-1,except that, as the zinc alloy powder of the negative electrode, zincalloy powder was used, which had an average particle size of 135 μm, waspassed through a 35-mesh sieve, was passed through a 200-mesh sieve in aratio of 20 wt %, and an apparent density of 2.9 g/cm³.

COMPARATIVE EXAMPLE 2-1

An AA alkaline battery was produced in the same way as in Example 2-1,except that, as the alkaline electrolytic solution for forming anegative mixture and the alkaline electrolytic solution for injection,36 wt % of a potassium hydroxide aqueous solution containing 2.4 wt % ofzinc oxide was used. At this time, the total water amount in the batterywas 0.247 g based on 1 g of positive active material.

COMPARATIVE EXAMPLE 2-2

An AA alkaline battery was produced in the same way as in Example 2-1,except that, as the alkaline electrolytic solution for forming apositive mixture, 42 wt % of potassium hydroxide aqueous solutioncontaining 2.9 wt % of zinc oxide was used. In this battery, theconcentration of potassium hydroxide of the electrolytic solutioncontained in the positive mixture before assembly of the battery was33.5 wt % considering the water contained in manganese dioxide, and theamounts of potassium hydroxide and water were 2.3 wt % and 4.4 wt %,respectively, with respect to the total weight of the mixture includingthe electrolytic solution. Furthermore, the total water amount in thebattery was 0.270 g based on 1 g of the positive active material.

Regarding 5 batteries of each of Example 2-2, Comparative Example 2-1,and Comparative Example 2-2, the water amount contained in the positivemixture after 3 months after assembly and the concentration of potassiumhydroxide of the alkaline electrolytic solution contained in thepositive mixture were obtained in the same way as in Example 2-1. Table2-2 shows these results, and the results of the battery of Example 2-1together with the total water amount (converted to the amount based on 1g of a positive active material) in the battery.

The batteries of Examples 2-3 and 2-4 were measured for only the wateramount contained in the positive mixture. However, similar results tothose of Example 2-1 were obtained. Accordingly, the results are notshown in Table 2-2.

TABLE 2-2 Water amount Concentration of in battery Water amountpotassium hydroxide (g/1 g of positive (wt %) (wt %) active material)Example 2-1 8.9 38.0 0.261 Example 2-2 9.1 36.9 0.268 Comparative 8.240.8 0.247 Example 2-1 Comparative 8.3 33.3 0.270 Example 2-2

As is shown in Table 2-2, in the batteries of Examples 2-1 and 2-2, thewater amount contained in the positive mixture was in a range of 8.4 to10 wt %. Thus, an amount of water sufficient for a reaction of thepositive active material was allowed to be contained in the positivemixture. Furthermore, the concentration of potassium hydroxide of theelectrolytic solution contained in the positive mixture also was allowedto be set in a desirable range of 35 to 39.5 wt %.

Next, each battery of Examples 2-1 to 2-4, and Comparative Examples 2-1to 2-2 was measured for load characteristics, battery temperature at atime of occurrence of a short circuit, and storage characteristics athigh temperature.

The load characteristics were evaluated as follows. A pulse dischargingtest was performed. In this test, a base discharging current was set tobe 0.5 A, and a pulse current of 2 A was allowed to flow for 2 secondsat an interval of 30 seconds. Then, the number of pulse dischargingcycles required for a voltage, at a time when a pulse current of 2 Aflowed, to decrease to 1.0 V or less was obtained.

The battery temperature at a time of occurrence of a short-circuit wasevaluated as follows. A thermocouple was fixed to the central portion ofthe side surface of the outer package can of the battery with analuminum tape. The surface temperature of the outer package can afterthe battery was short-circuited was measured, and evaluated based on thehighest temperature after a short-circuit. The batteries of Example 2-2and Comparative Example 2-1 were measured for a change in ashort-circuit current with passage of time, as well as the surfacetemperature of the outer package can.

Regarding the storage characteristics at high temperature, a change in adischarge capacity before/after storage at high temperature was checked,and the degree of degradation of battery's characteristics at a capacityretention ratio was evaluated. More specifically, the battery wasdischarged at a discharging current of 1A, and the discharge capacitybefore the battery voltage reached 0.9 V was measured. This measureddischarge capacity was determined as a discharge capacity beforestorage. Furthermore, a battery different from the above battery wasstored in a thermostatically controlled environment at 60° C. for 20days. Thereafter, the battery was cooled at room temperature for oneday. Then, the battery was discharged at a discharge current of 1A, andthe discharge capacity was measured before the battery voltage reached0.9 V. This measured discharge capacity was determined as dischargecapacity after storage. Then, the ratio of a discharge capacity afterstorage with respect to the discharge capacity before storage wasobtained, and this ratio was determined as a capacity retention ratio,whereby storage characteristics at high temperature were evaluated.

Table 2-3 shows the measurement results of the number of pulsedischarging cycles, the highest temperature of the surface of the outerpackage can, and the capacity retention ratio. Furthermore, changes inthe surface temperature of the outer package can and a short-circuitcurrent of the batteries of Example 2-2 and Comparative Example 2-1 werethe same as those in FIG. 3 and FIG. 4, respectively.

TABLE 2-3 Highest surface Number of pulse temperature of Capacitydischarging cycles outer package can retention ratio (No.) (° C.) (%)Example 2-1 62 123 88 Example 2-2 68 113 81 Example 2-3 68 112 89Example 2-4 73 138 91 Comparative 60 162 90 example 2-1 Comparative 67109 73 Example 2-2

In the batteries of Examples 2-1 to 2-4 according to the presentinvention, by setting the amount of water contained in the positivemixture to be 8.4 to 10 wt %, even though the total water amount in thebattery decreased to 0.23 to 0.275 g based on 1 g of positive activematerial, excellent load characteristics were obtained, the generationof heat at a time of occurrence of a short-circuit of a battery wassuppressed, and characteristics during storage at high temperature wereimproved. Particularly, in the battery of Example 2-3 containing 6 wt %of powder of 200 mesh or less in zinc alloy powder, in which the ratioof minute particles was larger than that of Example 2-1, the contentratio of indium, bismuth, and aluminum were optimized, whereby loadcharacteristics were enhanced compared with those of the battery ofExample 2-1, without increasing a temperature due to excess heatgeneration and decreasing a capacity retention ratio. Furthermore, inthe battery of Example 2-4 in which the ratio of minute particles wasincreased compared with Example 2-3, although the temperature of thebattery was increased slightly, load characteristics were increasedfurther while excellent storage characteristics at high temperature weremaintained.

On the other hand, in the batteries of Comparative Examples 2-1 and 2-2in which the amount of water contained in the positive mixture did notreach the above range, heat generation at a time of occurrence of ashort-circuit was large, and the battery temperature increase was large,or the storage characteristics at high temperature were degraded. Thus,practical characteristics were not obtained in either case. Regardingthe increase in temperature at a time of occurrence of a short-circuit,as shown in FIGS. 3 and 4, in the battery of Example 2-2 of the presentinvention, a short-circuit current was decreased within a short periodof time, so that heat generation was small, and the increase intemperature of the battery was small. In the battery of ComparativeExample 2-1, a short-circuit current was decreased slowly, and heatgeneration was increased to substantially raise the battery temperature.

As described above, in the present embodiment, by optimizing the amountof water contained in the positive mixture, the total water amount inthe battery system can be reduced, whereby an alkaline battery can beprovided which has desirable load characteristics, has high safety at atime of occurrence of a short-circuit, and has desirable storagecharacteristics at high temperature.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. An alkaline battery comprising a positive mixture molded in a ringshape comprising at least one selected from manganese dioxide and anickel oxide as a positive active material and a negative mixturecomprising a negative active material, wherein the positive mixturecomprises an alkaline electrolytic solution comprising potassiumhydroxide, an amount of water comprised in the positive mixture is 8.4to 10 wt % with respect to a total weight of the positive mixtureincluding the alkaline electrolytic solution, and the negative activematerial is zinc alloy powder, and a ratio of the zinc alloy powder thatpasses through a 200-mesh sieve is 4 to 40 wt % with respect to a totalweight of the zinc alloy powder.
 2. The alkaline battery according toclaim l , wherein the zinc alloy powder comprises at least one selectedfrom indium, bismuth, and aluminum.
 3. The alkaline battery according toclaim 2 , wherein contents of the at least one sciected from indium,bismuth, and aluminum comprised in the zinc alloy powder arc 0.03 to0.07 wt %, 0.007 to 0.025 wt %, and 0.001 to 0.004 wt %, respectively.